Justification:
This species is restricted to a single location (the Belize Barrier Reef World Heritage Site) and has an estimated extent of occurrence (EOO) of 203 km² and an area of occupancy (AOO) of 24 km². It is dependent on a unique combination of shallow coral and mangrove habitat, especially for juveniles. Significant habitat loss is occurring due to mangrove and coral removal for extensive coastal development within its very restricted range.

Since its original publication on the Red List in 2008, a new major threat has evolved in the spread of the invasive Lionfish, (Pterois volitans) which now encompasses the entire region of the greater Caribbean. Recent studies have revealed that Halichoeres socialis constitutes half of the Lionfish diet, with both juveniles and adults being consumed. Although a quantified population decline is not yet known, studies conducted elsewhere in areas of high Lionfish density have demonstrated reef fish biomass declines of 32-65%. Due to its predominance in the diet, this species is likely experiencing a much higher decline than the average reef fish. Since Lionfish populations off Belize have the potential to grow in density, this threat is expected to increase in magnitude.

Since the number of mature individuals and rate of decline are not known at this time, the species is listed as Endangered (EN B1ab(i,ii,iii,v)+B2ab(i,ii,iii,v)). Research is urgently needed on this species' population status, as it may qualify for a higher level of extinction risk. Furthermore, immediate conservation action is needed that implements Lionfish control measures and prevents destruction of its sensitive habitat.

This species is only known from the Caribbean Sea on clear-water reefs around inshore mangrove islands of the Belize Barrier Reef World Heritage Site, especially around the Pelican Cayes (Lobel et al. 2009). Its estimated AOO is 24 km² (calculated by clipping the distribution polygon to the WCMC 2013 coral layer). Its estimated EOO is 203 km² (based on a minimum convex polygon drawn around the extent of its range on the coral reef layer).

Currently, population size and trends have not been assessed. From the original description, it may seem that the population numbers are high, as juveniles are abundant where they occur. However, adult individuals are rarely observed.

The population is very likely suffering rapid declines due to predation by the invasive Lionfish (Pterois volitans) on both adults and juveniles; however, this decline has not yet been quantified (Rocha et al. 2015). Since the first Belizean sighting occurred in 2008, this threat has been growing with the rapidly increasing Lionfish population over the past seven years. Studies conducted in areas with high densities of Lionfish (Bahamas) have documented reef fish biomass declines of 32-65% over a period of two years (Green et al. 2012, Albins 2015). Belizean Lionfish populations have the potential to continue to increase in density (Chapman et al. 2013, Hackerott 2014); therefore, Social Wrasse population declines are expected to continue as well as increase in magnitude into the future.

Adults are reef associated and juveniles are mangrove and shallow reef dependent. It is found in shallow coral reefs over coral, sand, rubble or seagrass substrata (Randall and Lobel 2003) to depths of 10 m. Juveniles feed on zooplankton and form evasive, compact schools when threatened (Randall and Lobel 2003). Life history traits (longevity and age of maturity) are based on similar species in this genus of similar size. Its estimated larval life is two to three weeks; however, it may not be able to disperse outside the known area given the lack of suitable habitat.

This species is threatened by habitat destruction occurring throughout its range: extensive mangrove and coral removal and dredging activity related to coastal and resort development has been occurring since at least 2003. Since it was first assessed in 2008, the invasive Lionfish has been added as another major threat. Due to its small size, schooling, and hovering behaviour, it is easily and frequently targeted (Green and Cote 2014). In a study conducted throughout the range of H. socialis, it comprised almost half of the Lionfish diet, with both juveniles and adults being consumed (Rocha et al. 2015).

Population declines have not yet been quantified; however, studies in the Bahamas have observed a 32-65% decline in reef fish biomass over a period of two years due to predation by the invasive Lionfish (Green et al. 2012, Albins 2015). A study conducted in the same area by Ingeman and Webster (2015), found that local populations of Gramma loreto (also a common prey item of the Lionfish) face an elevated risk of extirpation as a result of increased predation. Based on these data, the population decline is suspected to be rapid and likely increase into the future as the Lionfish population density grows off Belize.

The Pelican Cayes are designated as a World Heritage Site, but no actual protective measures are enforced. Given its very small range, ongoing habitat loss, and susceptibility to invasive Lionfish predation, this species should be monitored and conservation measures implemented. Targeted Lionfish removal is greatly needed in this area (Rocha et al. 2015).